Low glare louver

ABSTRACT

A low glare louver constructed of a grid of cells made of transparent material produces a low brightness ceiling by controlling the light from the light source. The opposite surfaces of each beam of the grid slope downwardly producing a thicker base for forming a multiprism lens or a cylindrical lens.

llnited States Patent Mizuo Okada Kozagun, Japan Dec. 10, 1968 Aug. 17,1971 Mitsubishi Rayon Company, Limited Tokyo, Japan Dec. 11, 1967, Dec.25, 1967 Japan 42/103476 and 42/108002 inventor Appl. No. Filed PatentedAssignee Priority LOW GLARE LOUVER 6 Claims, 13 Drawing Figs.

US. Cl 240/78 LD, 240/46.39, 240/l06.1

int. Cl F21s1/06 Field of Search 240/78 LD, 46.39,106,106.1

[56] References Cited UNITED STATES PATENTS 2,143,149 1/1939 Guth 240/78LD-7 2,904,673 9/1959 Guth, Sr. 240/78 LD-7 2,927,994 3/1960 Guth, Sr.240/78 LD-7 2,971,083 2/1961 Phillips et a1. 240/78 LD-7 2,996,6098/1961 Wilson 240/78 LD-7 3,179,797 4/1965 Franck 240/78 LD-7 PrimaryExaminer-Samuel S. Matthews Assistant Examiner-Richard M. SheerAtt0rneySughrue, Rothwell, Mion, Zinn & Macpeak ABSTRACT: A low glarelouver constructed of a grid of cells made of transparent materialproduces a low brightness ceiling by controlling the light from thelight source. The opposite surfaces of each beam of the grid slopedownwardly producing a thicker base for forming a multiprism lens or acylindrical lens.

l l l l PATENTED Aus I 71971 SHEEI 1 OF 4 o o f 3; a m

MIZUO 0KADA,|NVENTOR. BY L ZM M {W ATTORNEYS PATENTEflAusmsn 3 600 570SHEET 3 or 4 I INVENTOR mzuo 0mm PATENTEBAusmsn 3600.570

SHEET 4 [1F 4 LIGHT msmmunou CURVE. HGI} SAMPLE LOUVERNoLSOURCEBRIGHTNESSOFTHELIGHTZOWxZLIGHTS.

msmucs 0=3oo mm INVENTOR MQIZUO OKADA BACKGROUND OF THE INVENTION Thepresent invention relates to a louver by which the light rays from alight source are modified or controlled to lower the glare of the light.In particular the invention is directed to a low glare louver wherein agrid of cells made of transparent material is employed to lower theangle of incidence of the light transmitted from the light source.

' FIG. 7 is a cross-sectional view of the louver employing multiprismlens wherein the bottom surface is of a mat finish.

FIG. 8 is a cross-sectional view of a part of the louver employing acylindrical lens wherein the bottom surface is mat finish;

FIG. 9 is a cross-sectional view of the louver in accordance with thepresent invention adapted for use on a lighting fix ture;

FIG. 10 is a sectional view of the louver with the lighting fix- Ingeneral, a louver is required to remove the glare effect of 10 takealong the line in F 9;

a light source by refracting the light rays from the light source in adirection inclined at more than 30 from the ceiling face. This isdesirable from the viewpoint of human engineering.

angle of the light at more than 30, for example the low brightnesslouver disclosed by US Pat No. 2,971,083, but the utilization ofmetallizing on the surface of the beam of the grid has proven to be adeficiency. Owing to the metallizing on the surface of the grid beam,the light intercepted by the beam FIG. 11 is an enlarged explanatoryview of the cross section of the louver for explaining the formula (Ihereinafter referred to;

FIG. 12 is a diagram showing the light distribution In accordance withthe first embodiment of the present invention, and

FIG. 13 is a diagram showing the light distribution in ac cordance withthe second embodiment of the present mven tion.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, thelouver in accordance with the present invention employs beams of gridmade of transparent is reflected onto the ceiling and thereby partlyabsorbed. Thus material in the shape of cylindrical lens or multiprismFens the brightness on the illuminated surface is lowered. And

moreover, metallizing the louver has proved to be expensive.

In other attempts to solve these problems in the prior art,

there has been provided a simple grid-shaped construction The beam of agrid employed in the present invention is preferred to be made of methylmethacrylate resin which has good transparency. although for example,inorganic glass, styrene resin or vinyl chloride resin could be emplovedThe made of opaque Synthetic resin This type of louver operates sidesurface 1 ofthe beam ofthe grid is required to form a cur at adisadvantage since the brightness on the illuminated surface is lowereddue to absorption of the light by the louver itself.

SUMMARY OF THE INVENTION A grid of cells made of transparent material isutilized to lower the glare of the light in the louver in accordancewith the present invention. In a luminair'e having a light source suchas fluorescent or incandescent lamps, the light from the light source isrefracted in limited directions to achieve the desired condition ofillumination. The resulting brightness on the illuminated surface isboth uniform and adequate. Since the grid of the louver is constructedof transparent material, the light from the light source is not absorbedby the louver and a high intensity level of brightness is obtained onthe illuminated surface.

It is an object of the present invention to provide a low glare louverfor producing a uniform brightness on the illuminated surface andlowering the glare of the light.

Another object of the present invention is to provide a low glare louveremploying transparent material wherein the light from the light sourceis not unduly absorbed by the louver and high brightness is obtained onthe illuminated surface.

A still further object of the present invention is to provide a lowglare louver which is capable of spreading the light from the lightsource and producing a restful source of light for the eyes.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an explanatory view showingthe projected light range produced by the louver in accordance with thepresent invention;

FIG. 2 is a partial plan view of a louver employing the mulvature thatwill have the beam thinner at the upper portion thereof as shown in FIG.3. Thus, the light from the llgh' source will be directed in a directioninclined at more than *0 with the ceiling face, the range of which isshown In Flt l and the light path of which is shown in FIGS. 4 and 5 We'Iu merals shown in FIGS 4 and 5 denote the angle in which the lightadvances respectively through the louver In this case a natrium D-lineof 5893 angstrom wavelength is used as the light with a louver made ofmethyl methacrylate resin The shape of the curve presented by the sidesurfaces of the beam of the grid is formed into a particular shaperepresented by the following formulas:

H=P -ltan 2(n1) sin 1/5 6 v3 R --1 Sm (,5 R 16 (2) 3 mm.H100 mm. (3)

wherein P is the pitch. H is the height of the beam R is a radius ofcurvature of the cylindrical lens or the circumscribed cylinder aboutthe multiprism lens, and n is the index of refraction of the employedtransparent material.

FIG. 11 explains the meaning of the formulae The light comes into thelouver from the point D at the top of the beam having a pitch P, heightH, radius of curvature R. and index of refraction n, it travels to thecenter E of the bottom of the adjacent beam through the center beam Mwhich refracts the light ray. The light is inclined at 30 when it leavesthe bottom surface of the beam of the louver. The path of the light andthe curvature of the surface of the louver are formularized as follows:

Refraction at the portion M can be regarded as a refraction tiprism lensin accordance with an embodiment of the present at a pnsm havmg an anglewh'ch m comac wnh the invention;

FIG. 3 is an enlarged cross-sectional view of the louver in accordancewith the present invention taken along the line A-A or B-B ofFIG. 2;

cylindrical lens at a point K on the surface thereof Since the triangleFGJ is similar to the triangle IGK, the angle GIK is equal to a(one-half of the angle of the prism) The distance KL is substantiallyequal to-P/ /5 since the prism FIGS. 4 and 5 are enlarged explanato ycross section views is thin Therefore: an equation Sin pump/W) obainedof the louver showing the transmitting effect on the light rays from thelight source;

FIG. 6 is a cross-sectional view of the louver employing cylindricallens in accordance with the present invention;

with reference to the triangle IKL.

Thus, the following equation is obtained,

a=sina R The declination of a thin prism having a top angle of 2a is(n-l )Za, therefore, the declination at M becomes 1 P 2 n1 -sin' V3 Rand the angle [3 becomes In order for the light which passes through thepoint E to pass through the point K shown in FIG. 11 the followingcondition is obtained:

B ZE -1 (i.)} H P tan B-P tan 2(n 1) sin B R which is written as followsLE) w/ R 16 That is, the top angle 2a is desired to be 17/8 or 22.5 orsmaller.

As to the height H in the formula (I), there is a limitation since thelouver is apt to be distorted or bent if too low, and apt to be tooexpensive due to the increase of the amount of the material if too high.Therefore, the height of the louver is required to be limited to therange indicated by the following formula from a practical viewpoint.

a=sin- 3mm.H100 mm. (3)

By designing a louver according to the above formulas, a small percentof the light from the light source will be directed in a directionincluded in the glare zone Z, (indicated with stippling in FIG. 1). Butsuch a small degree of light will not fatigue the eyes but will ratherproduce a soft and calm illumination effect.

The bottom surface 2 of the beams of the grid employed in the louver canbe mat finished while leaving the other surfaces mirror finished asshown in FIGS. 7 and 8. By providing this mat finish on the surface ofthe bottom of the louver in the multiprism or cylindrical lens shape,firstly, the light passing through the louver will be broadly dispersedand thus provides softer illumination effect and, secondly, the lightpassing through the louver will easily come out from the nadir of thelouver walls because of edge-lighting effect and thus provides a highdegree of efficiency.

Some embodiments in accordance with the present invention will bedescribed hereinafter, but the invention is not to be considered limitedto the following embodiments only.

EMBODIMENT 1 Methyl methacrylate resin is employed for the beam of thegrid of the louver in which the radius of curvature R is 80 mm., and thepitch P is mm. The height H is calculated to 15.3

A louver having a cross section of pentagonal shape was molded into thewedge shape beam of a grid by injection molding. The louver haddimensions fitted to the above formula (width 300mm., length 660mm.).

When the above-described louver was adapted to a fluorescent lampfixture as shown in FIGS. 9 and 10 (brightness of the lamp 20 w., thedistance d mm. between the louver 3 and the two fluorescent lamps 4, 4),the light distribution was measured as illustrated in the curves of FIG.12, wherein a solid line indicates the light distribution curve in aplane perpendicular to the axis of the lamp tube 4, broken lineindicates the light distribution curve in a plane parallel to the lamptube 4, and a dot-dash-line indicates the light distribution curve in aplane inclined at 45 with the lamp tube 4. Preferably, the distance dbetween the louver 3 and the lamps 4 is approximately the same as thedistance between the lamps.

As shown in the light distribution curves, almost all the light from thelight source is projected in the direction where the light range isinclined at more than 30 with respect to the horizontal plane. A smallpercent of the light falls out of the range, (inclined at 15 to 30 withthe horizontal plane) and helps make the louver body appear soft, andgentle to the eyes.

By making the bottom surface of the louver mat finished (320 mesh) asshown in FIG. 7, the distribution of the light remains as good as theunmatted surface while producing a softer illumination effect.

EMBODIMENT ll Using the same material as employed in the firstembodiment with a radius of curvature R of 100 mm., pitch P of 20 mm.and a height calculated as shown hereinafter, a louver having acylindrical cross section was obtained by injection molding. (width300mm. length 660mm.)

hll

When the louver made in accordance with the second embodiment was fittedto the fluorescent light fixture used in the first embodiment withdistance d from the light tube to the louver being 300 mm., the lightdistribution was measured with the results shown in FIG. 13. Althoughthe diagram of the light distribution curves are egg-shaped due to thedeep troffer 5 (reflector box) the light distribution characteristicswere almost the same as that of the first embodiment.

When the louver was molded by styrene resin (n=l .59) with the same moldpiece, the light from the light source was slightly dispersed into aspectrum due to the higher index of refraction n in comparison with themethyl methacrylate resin, but the control of the light direction wasbetter.

By matting the bottom surface of a louver made of methyl methacrylateresin by means of a sand paper of 0600, a softer louver was obtained.

The invention has been described in detail with particular reference tothe above preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention as described hereinabove and as defined in the appendedclaims.

What I claim is:

1. In a luminaire having a light source, and a low glare louver made oftransparent material disposed beneath said light source and comprised ofbeams forming a grid of cells, each of said beams being formed into amultiprism with the cross section of each beam being thinner in theupper portion closest to the light source and thickest at the nadir,said beams serving to gradually refract the light from the light sourceas it wherein P is a pitch of the grid of cells, H is the height of saidbeams, R is the radius of curvature of the circumscribed cylinder aboutsaid multiprism, and n is the index of refraction of said transparentmaterial.

2. A low glare louver as defined in claim 1 wherein said multiprism lensis a cylindrical lens, and said R is the radius of curvature of saidcylindrical lens.

3. A low glare louver as defined in claim 2 wherein only the bottomsurface of said beams is mat finished.

4. A low glare louver as defined in claim 1 wherein only the bottomsurface of said beams is mat finished.

5. A low glare louver as defined in claim 1 wherein said transparentmaterial is a synthetic resin.

6. A low glare louver as defined in claim 5 wherein said resin is methylmethacrylate resin.

1. In a luminaire having a light source, and a low glare louver made oftransparent material disposed beneath said light source and comprised ofbeams forming a grid of cells, each of said beams being formed into amultiprism with the cross section of each beam being thinner in theupper portion closest to the light source and thickest at the nadir,said beams serving to gradually refract the light from the light sourceas it passes through a plurality of said beams such that most of thelight leaving said louver is inclined in a direction more than 30* froma horizontal plane, the dimension of said beams being given by theformulas wherein P is a pitch of the grid of cells, H is the height ofsaid beams, R is the radius of curvature of the circumscribed cylinderabout said multiprism, and n is the index of refraction of saidtransparent material.
 2. A low glare louver as defined in claim 1wherein said multiprism lens is a cylindrical lens, and said R is theradius of curvature of said cylindrical lens.
 3. A low glare louver asdefined in claim 2 wherein only the bottom surface of said beams is matfinished.
 4. A low glare louver as defined in claim 1 wherein only thebottom surface of said beams is mat finished.
 5. A low glare louver asdefined in claim 1 wherein said transparent material is a syntheticresin.
 6. A low glare louver as defined in claim 5 wherein said resin ismethyl methacrylate resin.